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Space Sickness
SPACE MOTION SICKNESS: A Review of the Literature.
by Lambert T Parker
March 1987
GEnie L.T.P.
CIS 76456,672
ICOA APARKE4
Plink OJS312
SPACE MOTION SICKNESS
This is the least threatening but the most bothersome of the
problems encountered by humans in their early encounter with
microgravity. It affects 40% to 50% of all space travelers in the
first day of flight, often in the first hour or so. Fortunately the
symptoms usually resolves itself within two to five days into flight.
Symptoms of S.A.S are similar to motion sickness on earth
consisting of general discomfort / queasiness, nausea, vomiting
vertigo, headache, malaise, drowsiness and lethargy. In spite of the
similarity, earthbound susceptibility to motion sickness has not
correlated with susceptibility to space sickness.
The first case of space sickness was reported by Cosmonaut
Gherman Titov during the first long-duration flight of 25 hrs & 18 min
with a total of 17.5 orbits in aug of 1961. While other soviet
Cosmonauts also reported this phenomenon it remained virtually unknown
to the Mercury and Gemini Astronauts. Were the Astronauts made of
sterner stuff? The reason became obvious during the Apollo missions
when the crew were plagued with space sickness.
Explanation: Soviet crafts were larger than their first American
counterparts. As long as they remained strapped up in confined area
all was well but with increased area to move around, free-floating set
off the syndrome in 40-50% of them.
Not only did the did the syndrome affect some and spare others,
its symptoms and duration varied among the affected individuals. While
some had brief episodic vomiting without nausea, others had nausea
only. As stated by William Thornton, M.D, a member of the Discovery
mission: in no one was motor control affected, nor did any episode
last longer than 72 hours.
Data from Skylab flights STS-4 thru STS-8 showed that the
affected individuals did not have visual illusions, disturbed
oculomotor function , no change in intraocular pressure or in evoked
potentials, indicating that space sickness was not due to disorder of
end organs or originate in the central nervous system.
Space sickness monitoring experiments performed on Spacelab 1
showed that symptom intensity was clearly modulated with head movement
(especially pitching and rolling head movements), and was exacerbated
by reorientation illusions caused by ambiguous visual cues ( viewing
another crewman in an unusual orientation-eg:walking upside down or
traveling thru the tunnel connecting Spacelab with the Orbitor.).
Tactile and proprioceptive contact cues provided by wedging the
body into a corner or a bulk cubicle were palliative as was closing
the eyes, provided these contact cues were simultaneously present.
Even though Spacelab 1 crew judged helpful the use of transdermal
patches containing scopolamine, dextroamphetamine and metoclopramide
in reducing discomfort with only minimal side effects only few
suffers find relief.
PROPOSED MECHANISM FOR SPACE SICKNESS:
# Fluid Shift.
# Sensory Conflict
Sensory-conflict theory which is in current favor hold that due
to novel set of sensory cues produced by head motion in microgravity
causes an Otilith organ-canal and visual conflict sending conflicting
signals to the brain resulting in space sickness.
Background:
The organs of balance, motion sensation, and orientation
consist mainly of the Otolithic organ [macula] and fluid filled
semicircular canals. The semicircular canals sense fluid shifts caused
by head turning and generally behave normally in space. The crystals
of calcium carbonate [otolith] 3-19 micrometer in length are embedded
on a membrane which contains an array of hair cells which transmits to
the brain sensory signals that indicate the heads position and permits
recognition of vertical direction as per the pressure exerted by the
overlying otolith due to gravity during normal head tilting.
Hypothesis:
The central nervous system contains a neural storage center of
information from previous experience. Incoming sensory signals are
evaluated in light of previous information. When the sensory
information does not correlate with previous experiences, a NEURAL
MISMATCH occurs that affects the autonomic nervous system and results
in space sickness.
The nerves surrounding the otolith transmit sensory signals to the
brain indicating head position. When head tilts downward, the otolith
follows, sending a downward tilt signal. In microgravity the downward
tilt does not displace the otolith. The otolith remains in the
vertical plane but in a slightly different lateral position. When the
space traveller looks down- tilts his head downward vertically- the
otolith remains in the vertical plane with slight lateral displacement
sending signals to the neural center that the head has moved
laterally. Although he may know that he lowered his head to see the
floor. he feels as though he has turned from facing one wall to look
at another.
The normal input to the brain from the semicircular canals and
visual sectors combine with the confused otolith signals in
microgravity to cause a neural mismatch for which there is no
previous experience to evaluate it against. The problem was further
compounded in the era of Apollo-Skylab when visual cues through out
the interior of the crafts were grossly altered to suite maximum space
efficiency with disregard to visual paradigm. Climbing the ladder to
get to the next section appeared as descending a ladder headfirst to
an observer. Up and down orientation in a mess. Some of the most
severe and acute cases of space sickness are said to be sparked by
visual cues unique to the space environment. The central nervous
system reacts by producing the symptoms of space sickness.
At present two avenues are being explored to deal with the above
problem.
# Biophysical Conditioning.
Based on the fact that space sickness usually resolves within 72
hours, presumably because the neural storage center has accumulated
enough information about the otolith's performance in microgravity to
reconcile the conflicting sensory signals.
Training procedure: Biogenic feedback, to increase adaptability
of the autonomic nervous system as a key to avoiding space sickness or
shorten the time of space adaptation. Recreate visual cues unique to
space and conditions of microgravity to precondition the nervous system
preflight.
Primate studies by the Soviets indicate that adaptability of the
autonomic nervous system is the key to avoiding space sickness.
(Contention of I.B.Koslovskaya, M.D in her report at Seventh
International Man in Space Symposium in Huston (early 1986).
# Pharmaceutical intervention.
Much data needed about electrolyte imbalance, drug distribution,
drug metabolism in microgravity before this becomes practical.
Multiple studies are presntly being done in many centers to
understand the basic mechanism which includes study of neurovestibular
connections and disturbed function via tiny electrodes placed in
animals vestibular nerve centers and various pharmacologic agents are
then introduced in an attempt to prevent abnormal neurovestibular
responses.
SPECULATION:
If decalcification is the rule in space perhaps the ototith
themselves may disolve in long stay in microgravity. No otolith no
space sickness??. If so what about return back to earth.
Is this a major problem? No! Any major settlement in space will
have gravity by rotation of station or colony. Note while microgravity
causes vestibular dysfunction men hopping about in one-sixth gravity
of the moon suffered no disorientation or vestibular dysfunction. This
would mean that, even though human beings evolved under normal earth
gravity, the otolith can still provide sensory guidance under limited
gravity.
***************************=END=***************************
This is part of an educational series on space medicine. It was first
published in the Spaceport RT on the General Electric database GEnie.
If any of the readers wish reference or have questions, I will be
happy to answer them or look it up. Due to time restraint I can not
promise promptness. If enough interest exist here for review articles
such as this I shall upload more of them.
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